Communication apparatus having power-saving communication function, and communication method

Abstract

A communication apparatus which starts communication using a power-saving function changes, with its communication counterpart, a key for a confidential mode and performs power-saving communication. When terminating the power-saving function, the communication apparatus returns, with its communication counterpart, the key for the confidential mode to the original one. Then, after returning the key for the confidential mode to the original one, the communication apparatus performs an IP address reassignment process.

What is claimed is: 
     
       1. A communication apparatus comprising:
 a communication unit having a power-saving function configured to initiate a transition to a power-saving communication state wherein the communication apparatus communicates with a first device; 
 an encryption unit configured to transition to a first encrypted communication state where a predetermined encryption key is used to communicate with the first device when the communication unit initiates the transition to the power-saving communication state and to transition to a second encrypted communication state where a different encryption key from the predetermined encryption key is used or an unencrypted communication state when the communication unit terminates the power-saving communication state, wherein the predetermined encryption key is not used before transitioning to the power-saving communication state; and 
 an address reassignment unit configured to broadcast a message for confirming overlap of a network address of the communication apparatus with a network address of a second device and to reassign a network address of the communication apparatus in a case where the encryption unit transitions to the second encrypted communication state or to the unencrypted communication state from the first encrypted communication state when the communication unit terminates the power-saving communication state, 
 wherein the communication unit communicates with the first device in the second encrypted communication state or the unencrypted communication state after the reassignment of the network address of the communication apparatus is completed. 
 
     
     
       2. The communication apparatus according to  claim 1 , wherein the predetermined encryption key is different from a first encryption key used in communication before transitioning to the power-saving communication state, and
 wherein the communication unit is configured to return to a communication state where the first encryption key is used when the communication unit terminates the power-saving communication state. 
 
     
     
       3. The communication apparatus according to  claim 1 , wherein if encrypted communication is not performed before transitioning to the power-saving communication state, the communication unit is configured to return to the unencrypted communication state without encrypted communication when the communication unit terminates the power-saving communication state. 
     
     
       4. The communication apparatus according to  claim 1 , wherein the power-saving function reduces power consumption at least during standby. 
     
     
       5. The communication apparatus according to  claim 1 , further comprising a detecting unit configured to detect a new communication apparatus which has joined a network which the communication apparatus joins,
 wherein the address reassignment unit reassigns the network address of the communication apparatus if the detecting unit detects the new communication apparatus after transitioning to the power-saving communication state. 
 
     
     
       6. The communication apparatus according to  claim 1 , wherein the communication unit is configured to communicate in an ad hoc network which allows communication apparatuses to perform direct communication. 
     
     
       7. A communication method by a communication apparatus, the method comprising:
 transitioning to a power-saving communication state where a power-saving function is used; 
 transitioning to a first encrypted communication state where a predetermined encryption key is used to communicate with a first device when the communication apparatus transitions to the power-saving communication state; 
 terminating the power-saving communication state; 
 transitioning to a second encrypted communication state where a different encryption key from the predetermined encryption key is used or an unencrypted communication state when the power-saving communication state is terminated; and 
 broadcasting a message for confirming overlap of a network address of the communication apparatus with a network address of a second device and to reassign a network address of the communication apparatus in a case where the communication apparatus transitions to the second encrypted communication state or the unencrypted communication state from the first encrypted communication state when the power-saving communication state is terminated, 
 wherein communication with the first device in the second encrypted communication state or the unencrypted communication state after the reassignment of the network address of the communication apparatus is completed.